A year after going public, the head of Watertown-based Tetraphase says the investment world has become far more receptive to antibiotic biotech firms like his.

Guy MacDonald, president and CEO of one of the few local biotechs working on drugs to treat infectious bacterial diseases, says of the March 22, 2013, IPO, “It was difficult.” Offering its stock at an initial price of $7 a share — at the beginning of what only later became a free-for-all of biotech IPOs — it wasn’t until late summer that it traded above $8 a share for more than a couple weeks in a row.

In the fall, the other major local player in the antibiotic field, Cubist Pharmaceuticals, acquired two smaller biotechs for $1.6 billion, raising the profile of antibiotics makers everywhere. Tetraphase’s stock today is trading at $12.39 a share, up almost 80 percent from its IPO.

“I think the world has changed from a year ago,” he said.

Today, Tetraphase (Nasdaq: TTPH) assured investors it’s on track with a late-stage trial of its most promising antibiotic, eravacycline. MacDonald said that 265 of the 536 patients with complicated intra-abdominal infections have already been enrolled at the 100 or so sites it has designated worldwide. Results are still expected in the first few months of 2015, although MacDonald said that if enrollment keeps up as quickly as its been, they may come a little sooner.

The company also announced the beginning of another Phase 3 trial of the drug in patients with complicated urinary tract infections. That trial — which will treat patients with an intravenous drug first, then switch them to an oral one — is split into two parts. The first, involving 120 patients, will pinpoint the optimal dosage, then 720 additional patients will be tested at that dose level.

MacDonald said Tetraphase has also benefited from a September 2013 report from the Centers for Disease Control highlighting the need for new drugs to treat infections that have grown resistant to existing antibiotics. The “Antibiotic Resistance Threats in the United States, 2013” estimated that antibacterial resistance cause 2 million illnesses and 23,000 deaths every year in the U.S. alone.

“What they’re trying to do is get people’s attention that we’re not spending enough on antibacterial development,” said MacDonald. “And we’re not.”